1. Technical Field
The present disclosure relates to a vibration control device and a vibration control method used for a touch panel which vibrates in synchronization with a touch operation.
2. Description of the Related Art
In recent years, in various touch panel input apparatuses, such as a smartphone and a tablet terminal, including a touch panel, the touch panel has often been made to vibrate in synchronization with a touch operation (see, for example, Japanese Unexamined Patent Application Publication No. 2003-122507). Such vibrations of the touch panel may provide a touch operation with tactile feedback, and may complement an operational feeling (for example, a click feeling, a tactile feeling, etc.) obtained in a conventional key switch operation.
However, vibrations of a touch panel (hereinafter, referred to as “panel vibrations”, where appropriate) may be propagated to another part of the touch panel input apparatus, a desk on which the touch panel input apparatus is placed, or the like and may generate a vibration sound. Normally, the frequency of such a vibration sound generated by panel vibrations (hereinafter, referred to as a “panel vibration sound”, where appropriate) corresponds to the frequency of panel vibrations. Originally, panel vibration sound is unwanted sound and may make an operator and people around the touch panel feel discomfort.
A technique for producing panel vibrations at a frequency which is not easily propagated to human ears is described, for example, in Japanese Unexamined Patent Application Publication No. 2006-79136. Furthermore, a technique for making it difficult to hear a panel vibration sound by separately producing a high-frequency sound is described, for example, in Japanese Unexamined Patent Application Publication No. 2008-130055. The above techniques may reduce the discomfort caused by a panel vibration sound.
However, the related arts have a problem that it is difficult to achieve both a reduction of the discomfort caused by a panel vibration sound and maintenance of an operational feeling of a touch operation on a touch panel at the same time.
This is because the reasons described below. Normally, the audible range of human ears is between 20 Hz and 20,000 Hz. Meanwhile, the band of vibrations in which an operational feeling of a touch operation can be sufficiently obtained without adversely affecting other functions of a touch panel input apparatus is normally between about 50 and about 400 Hz (see Japanese Unexamined Patent Application Publication No. 2008-130055). That is, the frequency of panel vibrations which is able to provide an operational feeling mostly overlap with the audible range of human ears. Furthermore, a certain degree of vibration intensity is required to obtain an operational feeling, and therefore the volume of a high-frequency sound needs to be increased by the amount corresponding to the vibration intensity. That is, separately producing a high-frequency sound may make an operator and people around the touch panel feel more discomfort.